U.S. Pat. No. 5,368,107 discloses a vibration damper between the housing of a motor-driven chain saw as a first component and the handle thereof as the second component. The vibration damper is configured as a coil spring. Each of the ends of the coil spring is provided with an attachment element for fixing the coil spring to the housing and to the handle. The coil spring is held with turns at each end to the attachment elements. The fixing elements lie axially to the longitudinal center axis of the coil spring and are at a spacing with respect to each other. If the vibration damper breaks, the chain saw can be guided only with difficulty especially when the connection between the handle and the housing is completely lost.
It is an object of the invention to provide a vibration damper of the above kind which is so improved that an overextension of the vibration damper is avoided and it is still possible to guide the chain saw even when the vibration damper is broken.
The vibration damper of the invention is for mounting between first and second components of a portable handheld work apparatus. The vibration damper includes: a coil spring defining a longitudinal center axis and having first and second end portions; first and second attachment elements; the coil spring being securely attached at the first end portion with the first attachment element to the first component; the coil spring being securely attached at the second end portion with the second attachment element to the second component; the first end portion of the coil spring having several first turns and the second end portion of the coil spring having several second turns; the first end portion form-tightly engaging the first attachment element with at least a part of one of the first turns in the direction of the longitudinal center axis; the second end portion form-tightly engaging the second attachment element with at least a part of one of the second turns in the direction of the longitudinal center axis; the first and second attachment elements being disposed approximately on the longitudinal center axis and lying at a distance axially opposite each other; and, a coupling member extending through the coil spring to bridge the distance and the coupling member being connected to the first and second attachment elements so as to prevent the coupling member from separating therefrom.
When there is a break of the coil spring, a form-tight connection is maintained between the components connected by the vibration damper because a coupling member, which bridges the axial distance of the attachment elements, is arranged within the coil spring (between these attachment elements of the coil spring) and the coupling member is connected to each attachment element so that it cannot separate therefrom. The work apparatus can still be adequately reliably guided or held notwithstanding a break of the vibration damper.
It is practical to configure the coupling member as a rope and preferably as a steel rope. The rope is provided with respective holders at its ends and the holders have respective end faces facing toward each other. The holders engage form-tight behind respective edges of the attachment elements with these end faces. The rope assumes the emergency connection of the two components when there is a break of the coil spring in the region between the attachment elements. Furthermore, the rope limits also the maximum deflection of the coil spring and protects the vibration damper against overload.
If the rope is configured essentially as a thrust-stiff rope and especially as a steel rope, then the coupling member can be inserted simply in corresponding assembly or passthrough openings of the attachment elements. Additional guide measures or aids for threading as are needed for limp ropes are unnecessary.
The length of the rope is purposefully so dimensioned that it is greater than the distance of the edges of the attachment elements lying between the holders. The length of the rope is greater than the length of the unloaded coil spring. In this way, it is ensured that the rope does not limit the spring path of the vibration damper but does limit the possible spring path in the context of the permissible spring tension in each case and defines an effective protection against a tear-off when there is a break of the coil spring.
The holders are fixed at the ends of the rope and are advantageously guided in receptacle sections of the attachment element with slight radial play. These receptacle sections are configured to have a cylindrical shape.
In a preferred embodiment, at least one attachment element is provided with a lateral axial slot whose depth extends radially from the receptacle section up to the peripheral edge of the attachment element. The width of the slot is less than the maximum outer diameter of the holder which comes to rest in the receptacle section. The slot extends over the entire axial length of the attachment element so that the rope is guided radially to the attachment element through the slot into the attachment element and the holder can be fixed at the particular rope end in the receptacle section of the attachment element so that it cannot separate therefrom.
In an embodiment of the vibration damper which is simple to assemble, the receptacle section is so configured that its axial extension is greater than the axial length of the holder. For this reason, the holder can move in the axial direction of the attachment element and of the coil spring axially back and forth in the receptacle section. The maximum outer diameter of the second holder is therefore so selected that this diameter is greater than the maximum outer diameter of the first holder on the rope. The attachment element with the receptacle section for the second holder is provided at the base of the receptacle section with a through opening whose diameter is somewhat greater than the maximum outer diameter of the first holder. During assembly of the vibration damper, the rope with the first holder can be guided through the through opening at the base of the receptacle section for the second holder. The second holder is fixed in the receptacle section and the rope end with the first holder is guided through a slot from the peripheral edge of the other attachment element to the receptacle section in this attachment element where the first holder is fixed form-tight in the corresponding receptacle section.
The coupling member lies approximately centered in the coil spring in the assembled state of the vibration damper. It can also be practical to arrange the coupling member at a radial distance to the longitudinal axis of the coil spring in the proximity of the turns of the coil spring. The coupling member can be arranged at one end of the vibration damper loaded during operation of the portable work apparatus primarily in tension.